JCO Article Insights: HLA-Mismatched Unrelated Donor HCT With PTCy

In this JCO Article Insights episode, Alexandra Rojek provides a summary on "Post-Transplant Cyclophosphamide–Based Graft-Versus-Host Disease Prophylaxis Attenuates Disparity in Outcomes Between Use of Matched or Mismatched Unrelated Donors" by Schaffer et al published in the Journal of Clinical Oncology July 17th, 2024.

TRANSCRIPT

Alexandra Rojek: Hello and welcome to JCO Article Insights. I'm your host, Alexandra Rojek, and today we will be discussing an original report published in the October 1st issue of JCO titled, “Post-Transplant Cyclophosphamide–Based Graft-Versus-Host Disease Prophylaxis Attenuates Disparity in Outcomes Between Use of Matched or Mismatched Unrelated Donors,” by Shaffer et al.

The CIBMTR registry study set out to compare outcomes of patients undergoing allogeneic stem cell transplantation hematologic malignancies by HLA antigen matching status as well as by the type of GVHD prophylaxis regimen received either calcineurin inhibitor-based prophylaxis or post-transplant cyclophosphamide or PTCy. This study included patients reported to CIBMTR from January 2017 to June 2021 with AML, ALL or MDS, and required that they have undergone allotransplant with either a calcineurin inhibitor based so tacro or cyclosporine, GVHD prophylaxis, or PTCy, which included a calcineurin inhibitor or sirolimus with or without MMF and ATG. Matched unrelated donors were defined as an 8 out of 8 HLA match. And mismatched unrelated donors were defined as HLA mismatched at any single locus or 7 out of 8. The primary objective of the study aimed to compare overall survival or OS and GVHD and relapse-free survival (GRFS) within and between matched unrelated donors versus mismatched unrelated donors separated by calcineurin inhibitor versus PTCy based GVHD prophylaxis.

GRFS was defined as survival without grade 3 to 4 acute GVHD, moderate to severe chronic GVHD requiring systemic therapy or relapse. 10,025 patients were included from 153 centers, with a median follow up of over 36 months. Mismatched unrelated donor recipients were made up of 22% minority ancestry patients as compared to just 8% of patients receiving a matched unrelated donor allo transplant, showing an enrichment for patients of minority ancestry in the mismatched unrelated donor group. Just under 10% of patients were of minority ancestry in the study overall, reflective of challenges in transplant care for these patients, which may include inferior access to care, fewer available and suitably matched donors, among other factors. 54% of all patients were transplanted for AML and 29% for MDS. 45% of patients received myeloablative conditioning, 25% received regimens containing ATG, and 23% overall received PTCy with either a calcineurin inhibitor or sirolimus as well as MMF.

Among patients receiving PTCy, the authors did not find differences in overall survival by degree of HLA matching, whereas among patients receiving calcineurin inhibitor-based prophylaxis, there remained survival differences by HLA matching status. When comparing matched unrelated donor calcineurin inhibitor patients with PTCy matched unrelated donor patients, the PTCy arm had better OS, and the mismatched unrelated donor group who received PTCy had similar OS as well. For GRFS, matched unrelated donor and mismatched unrelated donor PTCy patients had no difference in GRFS, similar to the trend the authors see with overall survival. But these patients also had better GRFS than matched unrelated donor patients receiving calcineurin inhibitor-based prophylaxis. Within each prophylaxis arm, there was no difference in GRFS by HLA matching status. HLA mismatched patients receiving PTCy were less likely to experience GRFS than HLA mismatched patients receiving calcineurin inhibitor-based prophylaxis.

The authors saw similar differences in comparative trends when subgrouping patients based on conditioning intensity and additionally did not find differences in GRFS and OS by ATG exposure. When looking at patients with minority ancestry, those patients who received a match unrelated donor or mismatched unrelated donor with PTCy had comparable outcomes to non-Hispanic white patients. Additionally, among minority ancestry patients, there was a significant benefit in both GRFS and OS in the PTCy groups as compared to calcineurin inhibitor-based prophylaxis. When examining other specific toxicities included in the composite GRFS endpoint, such as GVHD rates among PTCy patients, the authors note that patients receiving a matched unrelated donor had similar rates of grade 3 to 4 acute GVHD but lower rates of moderate to severe chronic GVHD requiring systemic therapy. There appears to be signal that among PTCy patients, HLA matching reduced rates of moderate to severe chronic GVHD compared to mismatched unrelated donor patients receiving PTCy. These same trends also held when the authors looked at non relapse mortality with no significant differences within the PTCy groups by HLA matching status but reduced non relapse mortality compared to both calcineur and inhibitor-based groups.

However, notably, there was a greater risk of relapse among matched unrelated donor PTCy patients than matched unrelated donor calcineurin inhibitor patients, although this risk was comparable between mismatched unrelated donor patients by type of prophylaxis. The authors note that this has also been observed in other retrospective cohorts and may be confounded by differences in conditioning intensity between these cohorts of matched unrelated donor patients, affecting the risk of relapse. Finally, the authors also evaluate whether expansion of donor search criteria to mismatch donors from full HLA matching would increase availability of young donors from minority ancestry patients, and the study noted striking increases for all subgroups examined.

This study fits nicely with the BMT CTN 1703 trial published in the recent past, which has showed the superiority of PTCy with the calcineurin inhibitor and MMF when compared with conventional calcineurin inhibitor based immune prophylaxis for reduced intensity matched related donor and matched unrelated donor allotransplant. Of note, very few patients with one HLA antigen mismatch were enrolled on that study. However, others have shown the feasibility of PTCy in the mismatched unrelated donor setting, which has led to its adoption in practice. Although less than a quarter of patients included in this current study received PTCy overall, the findings clearly are aligned with the BMT CTN 1703 study, which is likely to change clinical practice in the longer term in this field.

As the accompanying editorial in JCO, written by Dr. Chakravarty nicely lays out, the differences between this study and the EBMT registry study, also published in this issue of JCO are subtle but worthy of note. While both studies show that mismatched unrelated donor patients had worse OS and GRFS than those receiving matched unrelated donor transplants, and then among matched unrelated donor patients the addition of PTCy improved GRFS and OS, there is discordance between the studies whether the addition of PTCy abrogates the effect of HLA mismatching on GRFS and OS. As this editorial points out, there are strikingly different rates of T cell depletion with ATG between the US and Europe, which may account for differences in comparator arms that lead to this discordance. There are several very exciting clinical trials ongoing that will aim to answer some of these outstanding questions regarding comparisons of PTCy and T cell depletion, which the field eagerly looks forward to reviewing.

In summary, this registry study of patients receiving allo transplant with matched unrelated donor or mismatched unrelated donor and calcineurin inhibitor or PTCy based GVHD prophylaxis, most notably shows that for patients who may not have a matched unrelated donor available, the addition of PTCy to a mismatched unrelated donor allo transplant allows for improved outcomes after transplant in toxicities and survival. This is most significant for patients of minority ancestries who usually have fewer matched unrelated donors available in registry searches. Improving the transplant options available to these groups of patients is of critical importance in improving equitable access to care for all of our patients. And this study, although retrospective in nature, provides an important understanding of our progress to date and suggests directions for future investigation may indeed be very feasible to continue to close these gaps in care for patients in need of an allo transplant for hematologic malignancies.

This is Alexandra Rojek. Thank you for listening to JCO Article Insights. Don't forget to give us a rating or review, and be sure to subscribe so you never miss an episode. You can find all ASCO shows at asco.org/podcasts.

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